The 12-1/4-in. directional application is one of the most challenging applications in North Kuwait. The section requires drilling from the Mutriba (Santonian) to Burgan (Albina) formations through highly interbedded, high-compressive-strength carbonates (limestone and dolomite), sandstones, and shales. In recent years, Kuwait Oil Company (KOC) has tested many different bit designs in an attempt to minimize stick/slip vibrations and maximize the rate of penetration (ROP). This paper presents the technology used to nearly eliminate stick/slip vibrations, leading to a field record (and a consistent performance) for this application, as well as the process used to develop the technology.
The interval was drilled using a rotary steerable system (RSS) to maximize wellbore quality and to provide consistent build-up rates (BUR) required. Parameters run in this application are often limited because stick/slip becomes uncontrollable when transitioning through the many formation types. In addition, reactive and stressed caving shales are regularly observed in the Ahmadi and Wara formations drilled during the interval. Special care is needed to mitigate these drilling challenges and to successfully drill the interval with low stick/slip vibrations and high ROP.
Using proprietary state-of-the-art design and analysis technologies, a new polycrystalline diamond compact (PDC) bit was designed for use specifically with RSS tools to minimize the vibrations. The solution required a thorough offset analysis before the interval that was presented using the design process. The design process enabled the presentation of a driller's roadmap to be used in conjunction with the new bit to enable a benchmark ROP to be achieved.
The use of the newly designed PDC bit produced minimal torsional vibrations, enabling a 62% increase in ROP over the field average. This increased ROP resulted in a savings of USD 90,000, reducing the cost per foot by 33%, as compared to the field average. The bit also came out in excellent condition, enabling future use in similar applications for KOC.